SPC AC 290559

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1259 AM CDT Fri Sep 29 2017

   Valid 301200Z - 011200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
   OF THE CENTRAL HIGH PLAINS VICINITY...

   ...SUMMARY...
   An isolated strong/severe storm or two may affect portions of the
   central High Plains vicinity Saturday afternoon/evening.

   ...Synopsis...
   Eastward progression of the upper flow pattern will continue across
   the U.S. Saturday, as an eastern trough moves rapidly east -- and
   eventually offshore, while a second/larger trough moves/expands more
   slowly east across the Intermountain West and into the Plains.

   At the surface, high pressure will largely prevail over the eastern
   half of the country, north of a west-to-east baroclinic zone
   lingering over the Gulf of Mexico and Florida Peninsula.  In the
   West, a cold front will advance across the Intermountain region,
   eventually reaching the northern and central High Plains where it
   will gradually overtake the prior/persistent lee trough.  This
   front/lee trough merger over the central High Plains may focus an
   area of afternoon/evening convective development.

   ...The central High Plains region...
   Modest low-level moisture return is forecast across the central High
   Plains area Saturday, as southerly winds strengthen east of
   sharpening lee troughing.  As mid-level heights gradually fall with
   the advance of the western U.S. trough, resulting large-scale ascent
   -- focused near the High Plains lee trough -- in conjunction with
   modest but sufficient afternoon destabilization (mixed-layer CAPE
   values likely reaching 500 to 1000 J/kg) may support development of
   isolated to widely scattered thunderstorms.

   With southerlies at low levels veering/increasing to southwesterly
   aloft, resulting shear will likely be sufficient for a few storms to
   organize/rotate.  Main risk -- given the relatively dry boundary
   layer and thus high cloud bases -- would appear to be hail and
   locally gusty/damaging winds.  Storms may expand in coverage through
   the evening, spreading eastward into the central Plains, within a
   broad zone of warm advection associated with nocturnal low-level jet
   evolution.  However, a cooling boundary layer suggests primarily
   elevated convection, and increasingly limited hail risk into the
   overnight hours.

   ..Goss.. 09/29/2017

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